An image carrier (on which an electrostatic latent image is formed) is provided in an electro photographic image forming device (for example, such as a laser printer). A developer cartridge for developing this electrostatic latent image into a visible image is removably installed in the laser printer.
The developer cartridge may include a developing roller that supplies toner to a photosensitive drum (which may or may not be part of the developer cartridge). The developing roller can contact or separate from the image carrier while the developer cartridge is installed in the laser printer. For example, in one conventional system, an engaging part is formed so as to protrude from the developing cartridge. The laser printer has a pair of grasping elements disposed on both interior sidewalls so that the pair of the grasping elements engages the engaging part. The laser printer also has a spring that urges one of the grasping elements towards the other grasping element. The laser printer further includes a cam that presses the other grasping element towards the one of the grasping elements. Thus, when the other grasping element is pressed by the cam, the one of the grasping elements presses the engaging part due to the force of the spring. Thus, the engaging part presses the developing roller against the image carrier. On the other hand, when the other grasping element is pressed by the cam, the one of the grasping element presses the engaging part so that the developing roller separates from the image carrier.
However, because a pressure force is placed on the same engaging part from the grasping element when the developer carrier presses on and separates from the image carrier and if the engaging part is not sufficiently strong, then the pressing and separating action of the developer carrier on the image carrier will not be reliable.